Our overall objective is to provide information on the difference between vertebrate and invertebrate stages of animal parasitic hemoflagellates and to gain an understanding of the transformation process between these stages. This involves study of nutritional and environmental agents important for regulation of hemoflagellate transformation. We have focussed on two hemoflagellates: Trypanosoma cruzi and Leishmania donovani. In the former we plan to study the mammalian factor(s) on infected host sera which inhibits transformation of bloodstream trypomastigotes to insect (and/or culture) stage "staphylomastigotes" and the insect cell factor(s) responsible for inducing the transition from insect stage "staphylomastigotes" to metacyclic trypomastigotes (see Lanar, 1979, J. Protozool.). In the case of L. donovani we plan to study respiratory metabolism of vertebrate stage amastigotes in vitro at 37 degrees C in the presence of hamster spleen transformation blocking factor(s) and to follow changes in polyamine metabolism during transformation from amastigotes to insect (and/or culture) stage promastigotes.